The main study hypothesis was that an organized, consistent program of dietary and lifestyle counseling would prevent excessive gestational weight gain. The sample size was chosen based on several criteria. The current literature states that 30–35% of women gain within the IOM guidelines. Our theory was that 30% of the women in the routine care group would gain within the IOM guidelines and that an increase of 25% (from 30% to 55%) of women in the intensive counseling group gaining within the IOM guidelines would be clinically significant. Therefore, using an 80% power and an alpha of 0.05, this required 61 participants in each treatment arm to achieve overall statistical significance.